thanks for answering janekm
No problem!
Some good info on your web page. I think I might try Enig finish with Storm or Seeed next time. I have used Seeed a few times and they are so cheap. But maybe I should tryStorm.
Storm aren't the cheapest but I use them for my employer and have had about 6 different boards made by them, all excellent quality. They also communicate very effectively.
I want to try some Arm Cortex chips maybe TQFP64 next time which should be 05mm pitch. I assume QFP is easier than QFN by hand.
http://www.keil.com/dd/docs/datashts/energymicro/efm32tg/d0071_efm32tg232_datasheet.pdf
Luckily they give the solder mask dimensions too.
I'm familiar with the Energy Micro chips, very nice devices! The peripherals in particular are very nicely and cleanly designed. I have only used the QFN and BGA packages from them but they have been no trouble to deal with.
QFP is indeed more practical to solder with a regular iron (I guess the flexibility of the leads ensures that they make contact with the pads on the PCB, with QFN it's easy to get contact with the PCB on one side and floating on the other). All the same, with hot air QFNs really aren't that difficult to solder.
The recommendation from some IC manufacturers though is to actually remove the soldermask entirely between the pads for 0.4mm QFN parts.
I seem to recall this, why would this make it easier? Flatness? I guess for 0.5mm I should go for soldermask.
It's to allow for the solder mask alignment tolerances when making the PCBs; having solder mask partially covering your pads could turn out very bad especially in volume manufacturing, so it's much better to leave the clearance. Leaving 0.1mm clearance results in no solder mask between the pads at 0.4mm pitch.
Also are you serious about the different colours, I assume you are, I really don't like green, is black ok?
I haven't had any issues with black and I do use it when it's needed for cosmetic reasons. The only time I have had real issues was when using white solder mask (there's an example picture on the article on my blog) and I believe the cause is the need for pigment to be added to the paint with white. All the same, green is the standard so if you use green it will go through the factories standard process which will be the one that is most tested.
Incidently I have a small amount of experience with chinese manufacturers I had my own mcpcbs made, they were fine but didn't test the manufacturing limits at all as they were for led bases. https://www.eevblog.com/forum/manufacture/metal-core-pcbs-from-zhejiang-zapon-electronic/
That post is very interesting actually, I have been curious about the cost of those metal core PCBs! Not that I have any need for them currently but it's always good to know.
This was the thread I referred to in my last post, not really worth reading.
https://www.eevblog.com/forum/eda/msop-clearances-for-seeed-studio/
In the post I was actually talking about MSOP, although in the final design I actually chose a different chip which was 045m DFN with a heat pad. Much harder. When they came back the solder mask was missing.
You're right I didn't actually drag solder that chip I did use hot air, and it took me a few tries.
I have had quite good luck lately using a line of solder paste (which invariably ends up being too much solder), reflow with hot air, followed by a quick drag solder to get rid of the excess solder.
If I absolutely need to ensure reliable soldering (and have the time) I use a different method using solder balls (as used for reballing of BGA chips), effectively turning the QFN part into a BGA part. It takes a lot of time but is very reliable, I should write up the method as I haven't seen it described anywhere.